From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 246F1C433EF for ; Thu, 2 Dec 2021 00:08:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354129AbhLBAML (ORCPT ); Wed, 1 Dec 2021 19:12:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38478 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354117AbhLBAKJ (ORCPT ); Wed, 1 Dec 2021 19:10:09 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3C829C061574; Wed, 1 Dec 2021 16:06:47 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 023BFB8219B; Thu, 2 Dec 2021 00:06:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92348C53FCF; Thu, 2 Dec 2021 00:06:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638403604; bh=kd/t6++JxJ1RnLpmjbHeu60p4SmLhAhEvhkN3dzIdP0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WegADlsKCIIvDWQfIlN+wUNr/Zisuw1YTnB90R+CUtgs4p/63HzvZer9mpIq0zgMx ABmdC3tqv3u/sFsJOvlkB7aXYjBUMTzun49ESn7aj1PYy+R9r8oiwWS8WxMTGIji1H oCEySto5x84IL4WLqQmBY7UCJkLHxWVpRaH0QoERz+H8Lv/nsqENwlbQOGy+JzYPJ0 HoZn5JSfIBTvaLRUzRwIpoTGiceNcOBgAO3t9/ekOMle5Oj3myrvYn/yw5f5pgWaCy H8G3WyFfeY8GZgvLjk078djsjUCP+vDQQNuCwR+aH7lkAr8Mwy4dtHG8C6ag4xA6Sx rL/CrSprZOajQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 51E0C5C1107; Wed, 1 Dec 2021 16:06:44 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH rcu 1/3] doc: Remove obsolete kernel-per-CPU-kthreads RCU_FAST_NO_HZ advice Date: Wed, 1 Dec 2021 16:06:40 -0800 Message-Id: <20211202000642.3126064-1-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20211202000540.GA3125972@paulmck-ThinkPad-P17-Gen-1> References: <20211202000540.GA3125972@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This document advises building with both CONFIG_NO_HZ=y and CONFIG_RCU_FAST_NO_HZ=y. However, CONFIG_NO_HZ=y offloads callbacks from all nohz_full CPUs, and CPUs with offloaded callbacks do not benefit from CONFIG_RCU_FAST_NO_HZ=y. Quite the opposite: CONFIG_RCU_FAST_NO_HZ=y simply adds a bit of idle entry/exit overhead. This commit therefore changes that advice to only CONFIG_NO_HZ=y. Signed-off-by: Paul E. McKenney --- Documentation/admin-guide/kernel-per-CPU-kthreads.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst index 5e51ee5b03589..e4a5fc26f1a9d 100644 --- a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst +++ b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst @@ -208,7 +208,7 @@ Do at least one of the following: 2. Enable RCU to do its processing remotely via dyntick-idle by doing all of the following: - a. Build with CONFIG_NO_HZ=y and CONFIG_RCU_FAST_NO_HZ=y. + a. Build with CONFIG_NO_HZ=y. b. Ensure that the CPU goes idle frequently, allowing other CPUs to detect that it has passed through an RCU quiescent state. If the kernel is built with CONFIG_NO_HZ_FULL=y, -- 2.31.1.189.g2e36527f23